Typically, the combustion condition of an engine is controlled such that the engine can rotate in the most possible stable and smooth manner. For example, for controlling the fuel injection amount such that the engine revolution speed becomes a target idling revolution speed at the time of start-up of the engine, such a method has been used in which the target idling revolution speed is accurately established in accordance with the progress of the warm-up condition of the engine (see Patent Reference No. 1, for example).    Patent Reference No. 1: JP-A-2002-364433